A variety of thermoplastic polyester polyurethane elastomers having generally satisfactory properties are known in the art. Such elastomers include polylactone polyurethane elastomers which are somewhat hydrolytically unstable and expensive. However, as far as is known, the only varieties of thermoplastic polyether polyurethane elastomers having satisfactory properties are those disclosed in U.S. Pat. Nos. 3,933,937 and 3,933,938.
U.S. Pat. No. 3,933,937 discloses, inter alia, a process for preparing an injection-moldable thermoplastic polyether polyurethane elastomer by (I) reacting an aromatic diisocyanate with a modified polyol (polymer/polyether diol) to produce a polyurethane quasi-prepolymer having a free NCO content of from 7 to 15 percent (preferably from 8 to 12 percent) and then (II) reacting said prepolymer with a short chain alkane diol to produce an injection molding-grade elastomer in the absence of a catalyst. However, the elongation and Die "C" tear strength of these elastomers are not as good as may be desired. U.S. Pat. No. 3,933,938 discloses a similar process for preparing a thermoplastic elastomer where a polyalkane ether diol (polyether diol) is used as an additional reactant in step (I) of U.S. Pat. No. 3,933,937 apparently to improve the tear strength and elongation of the elastomers. However, the only specific polyalkane ether diol disclosed in the patent (polytetramethylene ether glycol-"PTMEG") is expensive.
Moreover, quasi-prepolymers having relatively low free NCO contents, such as those disclosed in the above-mentioned patents, are of generally undesirably high viscosities and the resulting thermoplastic polyether urethane elastomers possess low to moderate flexural modulus (stiffness) and hardness. Further, the processess for producing thermoplastic polyether urethane elastomers disclosed in the abovementioned patents are characterized by relatively slow processing times.
Rapid processing times of less than one minute are known to be obtainable by simultaneously reacting and forming polyether polyurethane elastomer formulations using a process such as the Reaction Injection Molding (RIM) process. However, such formulations generally produce thermoset elastomers and so any scrap produced is relatively useless.
It is an object of this invention to provide thermoplastic polyether polyurethane elastomers having satisfactory properties (including elongation and tear strength) from relatively inexpensive starting materials.
It is a further object of this invention to produce thermoplastic polyether polyurethane elastomers having high flexural modulus (stiffness) and hardness from quasi-prepolymers having relatively low viscosities.
Another object of this invention is to provide a relatively rapid process for producing polyether polyurethane elastomers useful, for example, in the RIM process.
Still another object of this invention is to provide a polyurethane quasi-prepolymer that is useful in the RIM process.
These and other objects of this invention will become apparent from a reading of the following detailed specification.